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Is the ball speeding up?
Use three sensor readings from one ramp run to compare the time for two equal distances.
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Learning Outcomes
Distinguish elapsed time to a sensor from travel time between two sensors.
Subtract two elapsed readings to find the time for a section of track.
Use times for equal distances to compare the ball's average speed.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
1 · Two equal sections
4 min
A ball runs down a ramp. It may move too quickly for our eyes to judge how its speed changes. Sensors can help: each one records when the ball reaches it.
Does the ball cover 20 cm more quickly later in its journey?
We will choose a 20° ramp in the remote lab and watch a recording of a real experiment. Compare the section from 16 to 36 cm with the section from 36 to 56 cm. Both are 20 cm long.
Our two sections
The diagram shows distances along the track, laid out straight. The large circles mark the three readings we need; the small circles are the other sensors.
Tell a partner your prediction: will the later section take less time, more time, or about the same time? Keep your first idea until you see the readings.
2 · Collect three readings
8 min
The lab's t (ms) row shows elapsed time: time counted from the start to each sensor. The timer does not restart at every sensor. One millisecond (ms) is one thousandth of a second; keep all your readings in ms.
Open the Inclined Plane lab
Open the lab from this activity. Enter 20 in the angle control and press Tab. Check that it reads 20° before starting.
Select Start experiment now. Watch the ramp move into position and the ball travel past the sensors.
Wait for Drop results. Check that the reported angle is 20°.
Find 16, 36 and 56 in the d (cm) row. Copy the t (ms) number directly below each into the table here. Use all three readings from this one run.
After using the lab, return to this activity and mark the lab practice as done. Keep your three readings for the next step.
Fill only the three labelled rows below. Enter the elapsed readings, before doing any subtraction. Leave extra rows blank.
Elapsed readings from one 20° run
Copy three numbers from the lab's t (ms) row: one below 16 cm, one below 36 cm and one below 56 cm. Use a single run. Positions are already filled in; leave any extra rows blank.
| Sensor position | Elapsed reading ms |
|---|---|
3 · Find each section's time
8 min
A later clock reading includes time spent before that section. Subtract the reading at its start from the reading at its end.
For example, a bus passes one stop 8 minutes after leaving the station and the next stop at 13 minutes. The journey between those stops takes 13 − 8 = 5 minutes.
Use the same idea with your readings. You may use a calculator.
First 20 cm section: 16 → 36 cm
How long did the ball take from 16 to 36 cm? Enter your reading at 36 cm − your reading at 16 cm.
Later 20 cm section: 36 → 56 cm
How long did the ball take from 36 to 56 cm? Enter your reading at 56 cm − your reading at 36 cm.
For equal distances, less time means a higher average speed over that section.
What do your two section times show?
Compare the two times you calculated. Which conclusion matches them?
Tell your partner: “Both sections are 20 cm. The first took ___ ms and the later one ___ ms, so…” Then look back at your prediction. Check your table and answers, and submit the activity.
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